1. Field
This invention relates to electrical devices having a touch sensitive screen and, more specifically, to an electronic device having a touch sensitive screen wherein the touch detectors are disposed in a sparse pattern over the screen active area and in a dense pattern over the viewing area of the screen.
2. Description of the Related Art
As is well known in the art, users may interact with software or similar constructs through a display screen, or simply “screen.” That is, the screen is structured to display images of various command and control functions which the user selects with an input device. For larger electronic devices, such as computers, the user typically utilizes a keyboard and/or mouse. For smaller electronic devices, such as, but not limited to, personal digital assistants or cellular telephones, control was originally limited to a keypad, as a mouse or similar device was not included. Similarly, electronic devices used in public areas, such as, but not limited to, automatic teller machines, also used simple keypads and did not include input devices such as a mouse or a full keyboard.
Users, however, desired the simplicity and ease of use associated with mouse or similar input devices. Thus, one improvement over a simple keypad was the use of a touch sensitive screen. One type of touch sensitive screen included sensors in a transparent layer above the screen. This type of device, however, increased the thickness of the screen and reduced the screen's optical performance. “In-glass” touch sensitive screens, however, typically included a plurality of sensors 1 disposed within the screen 2 as shown in FIG. 1. It is noted that the sensors are shown schematically and are typically not visible to the naked eye. The sensors, which were typically capacitive, mechanical, or optical sensors, provided a signal when actuated. The sensors are actuated when an object, typically a stylus or a finger, is positioned on, or immediately adjacent to, the screen. The sensors are coupled to a sensor output device which is further coupled to a control assembly. The sensor output device and/or control assembly are structured to interpret the sensor signals to determine the position on the screen over which the object is located. Thus, for example, an electronic device could display an image representing commands, such as icons or a menu, and a user could use a stylus or a finger to select the command simply by touching the portion of the screen displaying the icon of menu. Further, the sensors could also, typically, detect a “tap” which indicated when a selection had been made.
A screen 2, such as, but not limited to, a liquid crystal display (LCD) panel 3, is typically disposed in a frame or housing. The LCD panel utilizes a liquid crystal medium to produce an image formed from a number of small, illuminated points, or pixels, located on a grid. The pixels are spaced as closely together as possible so that the image does not include voids or dark areas. Further, the pixels have an “aspect ratio” that represents the size of the pixel. The screen or LCD panel has an active area that is structured to display images. Disposed about the active area is an inactive area. There are no pixels in the inactive area. Because it is desirable to not have the image abut the frame, a portion of the inactive area is visible to the user. This area is also called the “viewing area.” Beneath the frame is a hidden portion of the inactive area that the user cannot see or touch.
As shown in FIG. 1, the sensors were typically disposed in a generally constant pattern over the entire active area and viewing area. This pattern is, typically, a dense pattern as the higher the number of sensors, the more accurate the touch sensitivity of the screen. That is, if the sensors were disposed in a sparse pattern, the accuracy of the sensor grid would be reduced and, for example, the controlling software may not be able to accurately identify which icon of menu item the user selected. The use of a dense pattern, however, is a disadvantage as the sensors required space in the active area and, to provide that space, the pixels had to have a reduced aspect ratio. This is a further disadvantage as the software, or other electronics, used to create the image can be structured to limit the locations of the menus or icon to specific portions of the active area, such as an area adjacent to the viewing area.
There is, therefore, a need for a touch sensitive screen for an electronic device that has a reduced number of sensors in the active area.
There is a further need for a touch sensitive screen for an electronic device that has a sparse pattern of sensors in the active area and a dense pattern of sensors in the viewing area.